Determining the Rate of Osmosis through a Semi-Permeable Membrane Schneider, Justin* Sec 16 and Thomas Hudson Introduction Water is the principle solvent in cells. There are three conditions that a cell may be subjected to in the cells physical environment. The cells may be isotonic, hypotonic, and hypertonic. Isotonic is when the cell and is environment have equal concentrations of solutes. Therefore cells in an isotonic solution do not experience osmosis.

When the cell is hypotonic it has a lower concentration of solutes so water will move out of the cell.When the cell is hypertonic, it will have a higher concentration of solutes and water will move into the cell to attempt to reach an isotonic state. The primary purpose of this exercise is to measure the rate and direction of osmosis under different concentrations. The greater the concentration of the solute (sucrose) the faster the solution (water) will pass through the membrane trying to achieve an isotonic state (Vodopich and Moore. 2011. ) Materials and Methods To start the experiment 8 pieces of string were gathered; approximately 2 inches in length, sewing thread were used for this experiment.Four water soaked pieces of dialysis tubing that were 15 cm long were also used.

A small beaker for bag A was filled with a solution of 25% sucrose, was labeled to keep separate from the other beaker. A larger beaker was used for bags B, C, and D. It was filled with a 1% solution of sucrose, and was labeled for good practice. Each end of the tubes was sealed by folding and tying it tightly with one of the pieces of thread. The other end of the tube was soaked with water and opened gently rolling it between the index and thumb fingers.

Once one end of each tube was sealed and the ends were opened each tube was filled with a solution. Before filling each tube with its selected solution a small piece of paper with a letter A, B, C, or D written in pencil were inserted so they could easily be identified. Once filled with its contents each bag was rinsed and dried to obtain an accurate weight. They were then weighed before they were put into the selected solutions. All the bags were filled with 10ml of a sucrose solution. Bags A, B, C, and D were filled with 1%, 1%, 10%, and 25% sucrose solution.

After each bag was filled the open ends were tied tightly and were placed into two separate containers, each filled with different sucrose concentration solutions. Bag A was placed the container with a 25% sucrose solution. Bags B, C, and D were placed in the container with a 1% sucrose solution. Once the bags were placed into each solution, a timer was started. At 15 minute intervals each one was taken out of the solution, they were then dried off and the weight was recorded.

This was so an increase or decrease in weight could easily be seen.Each bag was taken out, dried and was weighed at 15 minutes, 30 minutes, 45 minutes, and at 60 minutes to conclude the experiment. Results Both of the bags C and D were hypertonic to their surrounding environment. Because the sugar (Solute) couldn’t pass through the membrane it was only water going in or going out of the bags in the solution, which is the case for osmosis (Raven, et al. 2011. ) Bag A reduced in weight by 2. 8 (g) in 60 minutes.

The largest reductions in weight occurred in the first 30 minutes. In the 30 to 45 minute range it still dropped 0. 6 (g), and another 0.

in the 45 to 60 minute time period. Bag B did reduce in weight, which was unexpected because it was supposed to be isotonic with its surroundings, but the loss was minimal at 0. 7 (g) over the 60 minutes. Bag C reduced in weight a total of 4.

7 (g). Bag D did increase in weight but started to level out at the 30 minute interval. The total weight increase for bag D was 1.

1 (g). Figure 1. Changes in Weight of Dialysis Bags Bags A, B, C, and D were all filled with 10 ml of sucrose solutions of 1%, 1%, 10%, and 25%. Once the bags were in the solutions of sucrose a timer was started.At 15 minute intervals each of the bags were taken out of the solutions, dried off and the weight was recorded. Bag A was placed in a container with a 25% sucrose solution.

As the graph shows it reduced in weight meaning it expelled water trying to reach an isotonic state. Bags B, C, and D were placed in a 1% sucrose solution. Bag B was supposed to be isotonic with its environment, but as the graph showed reduced in weight slightly. Bag C had 10% sucrose solution, so it was hypertonic and should have increased in weight, but a leak was found in the bag resulting in a loss of weight.Bag D had a 25% sucrose solution and did increase in weight, but not as much as expected. Regardless it proved to be hypertonic. When bag D was tied there was not much extra room for the water to fill, therefore limiting the amount of allowed growth. Discussion Even though the relationship between bag B and its solution was supposed to be isotonic it would have been interesting to see how far off the solution really was.

The result that was found for bag B was a decrease of point seven (g). Bag A was still decreasing in weight by measurable amounts at the sixty minute interval when weighed.The total weight lost during the experiment of bag A was two point eight (g) which was still not showing an isotonic relationship to its environment. Other than the result of bag C the results were almost what were to be expected from this test.

In bag C had there not been a leak, it would have gotten heavier by water passing through the tubing to create an isotonic solution in theory. Another test should be conducted to acquire an accurate result. If the experiment would have been able to be restarted with lack of time restraints it would have been nice to see if it would show the expected results.

Bag D was filled and tied too tightly for this experiment. That being said in hindsight more room should have been allowed for the osmosis to occur. When the bag was filled up the bag was taught, there wasn’t enough room for much more water to enter. It would be good to remember when testing to see the results of a (cell) in a hypotonic solution to leave room for increases of volume. If there would have been more room for water to enter there would have probably been a greater increase in weight.

References Raven, Johnson et al. 2011. Biology. 9th edition.McGraw Hill.

New York, NY. Vodopich and Moore. 2011. Biology Laboratory Manual, 9th Edition. McGraw Hill. New York, NY.

Acknowledgements The author would like to thank Miss Kendra Hill for the education, and instruction. He would also like to thank Roel Rabara for his guidance and thorough instruction in the Biology 151 lab that has helped him understand how the scientific methods work as well as helping him improve his scientific research writing. Last but not least his lab partner Thomas Hudson who has helped find the results of their experiments and tests.


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